The present invention relates to an eyeglass lens grinding apparatus which grinds a lens to be processed, so that the lens fits into an eyeglass frame.
An eyeglass lens grinding apparatus is known, which, on the basis of input frame shape data obtained by a measurement of the shape of an eyeglass frame, grinds a lens to be processed to fit into the eyeglass frame. The apparatus is provided with lens measuring means for measuring the shape of the lens (the peripheral edge position) on the basis of the input frame shape data. The lens measuring means includes two detecting mechanisms respectively having first and second feelers that are movable in the direction of a lens rotary shaft and that are brought into abutment with the front and rear surfaces of the lens to detect their peripheral edge positions. Alternatively, the lens measuring means includes a single detecting mechanism by which the front and rear faces of the lens are sequentially measured. Such a lens measurement is performed for each of the lenses to be processed.
In a manufacturer of sunglass lenses, the sunglass lenses are generally processed such that lenses of the same specifications are continuously processed into the same shape. When the measurement of the lens shape is performed prior to each processing of a lens, there arises a problem in that the production efficiency is low.
Such an eyeglass lens grinding apparatus is known, which has a rough grinding wheel having a particle size of about #100 to #120 depending on the material of a lens to be processed, and a finishing grinding wheel having a particle size of about #400. These rough grinding and finishing grinding wheels are coaxially mounted on a grinding wheel rotary shaft. The finishing grinding wheel is provided with a single bevel groove. In the lens grinding apparatus, the lens to be processed is held on the lens rotary shaft, and pressingly contacted with the grinding wheels so that a bevel is finally formed in a peripheral portion of the lens. That is, the lens is roughly processed by the rough grinding wheel and then processed by the finishing grinding wheel having the bevel groove, into a final shape in which the lens fits into an eyeglass frame.
When the number of lenses to be processed is large, the degree of wear of a grinding wheel is increased in proportion to the number. Particularly when the finishing grinding wheel which is used in the final finishing processing is largely worn, this wear tends to produce an error in the finished size. Furthermore, wear of a grinding wheel reduces the processing accuracy due to a lowered processing performance of the grinding wheel.
In order to avoid the size error and reduction of the processing accuracy, the finished size must be periodically checked to make an appropriate size adjustment. For lenses such as sunglass lenses which are processed in large quantities by the manufacturer, however, frequent size checks result in a reduced production efficiency.